Annual stack tests do not give an accurate estimate of emissions during start-up, shut-down or upset conditions – which can be thousands of times higher than during steady-state operation (which is when stack testing is typically done).

Dioxin emissions many times higher during startup/shutdown periods, when dioxin emissions aren't monitored

The following was written by Alan Watson, CEng, for the Global Alliance for Incinerator Alternatives in relation to revisions to the Eurpean Union Directive on integrated pollution prevention and control:

We know that high dioxin emissions can be generated and released particularly during start-up periods (Gass, Lder et al. 2002; Nordsieck, Neuer-Etscheidt et al. 2003; Environment Agency 2006; Neuer-Etscheidt, Nordsieck et al. 2006; Tejima, Nishigaki et al. 2007; Wang, Hwang et al. 2007; Wang, Hsi et al. 2007; Chen, Lin et al. 2008). It is notable that these start-up periods are never monitored with spot dioxin tests although they are clearly a time when it would be anticipated that dioxins could be formed within incinerators from previously deposited carbonaceous deposits.

Tejima tested a modern Japanese incinerator and found that even a single incinerator start-up released more dioxins to air than operating the incinerator in steady state conditions non-stop for over 2 months. Contamination levels of ash were also increased. If an incinerator was started more than four times a year the majority of the dioxin emissions are likely to come from the unregulated start-up emissions.

The results from Wang are more worrying. To verify the PCDD/F characteristics of incinerators during start-up a continuous MSW incinerator was investigated for two years. The elevated PCDD/F emissions of the MSWI during start-up could reach 96.9 ng I-TEQ N m3 (nearly 1,000 times the EU limit of 0.1 ng/m3) and still maintained a high PCDD/F emission (40 times higher than the Taiwan emission limit) even 18 h after the injection of activated carbon.

From the four MSW incinerators they studied the estimated annual PCDD/F emission from normal operational conditions was 0.112 g I-TEQ. However they calculated that one start-up procedure can generate 60% of the PCDD/F emissions for one whole year of normal operations. Furthermore the PCDD/F emission from the start-ups of some incinerators was at least two times larger than that of a whole years normal operations. This was even without consideration for the PCDD/F emission contributed by the long lasting memory effect.

Continuous emissions monitoring for PCDD/F content offers the most accurate and reliable means for estimating PCDD/F releases and evaluating potential impacts on public health and the environment. One of the more important earlier studies of the AMESA system for monitoring PCDD/F releases in stack gases is that by De Fre and Wevers (1998). These scientists found that, in comparison to the AMESA system, the standard 6-8 hour sampling time "underestimated the average [dioxin] emission by a factor 30 to 50."

Subsequently, the AMESA system has not only been validated by the German EPA but is now in widespread use in Europe. For example, all municipal waste incinerators in the Flanders portion of Belgium are now required to use the AMESA method and, through such use, have demonstrated substantial reductions in dioxin releases to air. Reinmann et al. (2001) summarize as follows:

“In the last three years the continuous dioxin and furan monitoring system AMESA came to a standard for the continuous control of the dioxin emissions in waste incinerators in Belgium. Due to these results and the operators feedback, some new features were developed and results showed that the continuous emission control of dioxins and furans is necessary. … Actual results of the Walloon region of Belgium, where the continuous control of the dioxin emission is obliged since the 1st January of 2001 shows once again, that plants which were still controlled by short time dioxin measurements can have too high dioxin emission when they were controlled continuously.”

In a still more recent report, Reinmann (2002) concluded as follows:

“The actual results of the Walloon region of Belgium show the different advantages for all, the public, the environmental and the operator. If defects in the plant happen, which lead to higher dioxin emissions, these defects are recognised earlier and help to reduce the dioxin emissions. On the other side, if the values are constantly low, the public acceptance is higher and help to increase or to keep high the capacity of the plant. More and more countries start to think about a continuous control of the dioxin emissions of the waste incinerators. Therefore in different countries verification projects were started. If such regulations will be introduced global the dioxin emissions can be reduced world-wide in a strong way.”

With respect to the on-going application of the AMESA system at the 11 municipal waste incinerators in Wallonia in Belgium, Idczak et al. (2003) noted as follows:

“Evolutions of results since the launching of the programme show the benefits brought. Continuous monitoring with fast availability and publicity of results triggered efforts of operators. They managed their process and prevented breakdowns of their abatement system so that remaining problems are very limited. … Actually samples for 14 days periods are unquestionably more representative than sampling durations of 6 or 8h as usual with the manual method. Continuous sampling throughout the year is comprehensive.

Results of the quasi-continuous monitoring of dioxin releases in the stack gases of the 11 incinerators in Wallonia are available 2 weeks after sample collection and are posted on Environment Directorate’s web site at the authorities’ request.” [See http://environnement.wallonie.be/data/air/dioxines/]

The AMESA system has also been used for hazardous waste incinerators. For example, four years ago, Mayer et al. (1999) described in detail the use of the AMESA system, as required by German authorities, in a study of high- and low-temperature operation of a hazardous waste incinerator.

In summary, the AMESA system for the quasi-continuous monitoring of dioxin releases in incinerator stack gases is well proven and has accumulated a substantial record of successful application with solid documentation of the benefits of such quasi-continuous monitoring in comparison to the standard occasional 6-8 hour sampling period. While the development of other methods of continuous or quasi-continuous stack gas sampling and analysis is to be encouraged, there is no sound rationale for waiting for their development rather than using the AMESA system, which is already well-developed, widely used and well-proven.

Chachignon: Identification of Key Surrogates for Real-Time Dioxins Monitoring
2007 - France - Automatic continuous sampling devices for dioxin have been installed over the last ten years, but since they don't provide real-time reporting (results take about 2 weeks), they are lookng for something that is simpler to test for that would be a good indicator of dioxin levels - either a surrogate (one type of dioxin) or a precursor polychlorinated benzene/phenol. Found TEQ correlation coefficients >.92 for 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDD, 1,2,3,7,8,9-HxCDD and Cl6Bz. Suggests use of these monitoring devices: Resonance Enhanced Multi-Photon Ionization coupled with a Mass Spectrometer Time of Flight, gas chromatographs with Electron Captures Detector, on-line ion trap mass spectrometer.

Gullett: Transient PCDD and PCDF Concentrations in an MWC
2006 - USA - Tested dioxin precursors during different phases of boiler operation.
"The transient, upset conditions tend to promote PCDD formation. 52% of the TEQ value is due to PCDDs during startups, versus 39% during steady state operation."
"Large differences exist in PCDD/F levels in identical, parallel boilers... these differences suggest that even steady state conditions are amenable to process monitoring and control in order to minimize conditions that lead to PCDD/F formation."
"The rapidity of the response of PCDDs, PCDFs, and other co-pollutants to transients and the distinctions between similar boilers suggest that rapid on-line monitoring will be necessary to effect changes in operating conditions that will reduce or prevent favorable PCDD/F formation conditions. However, variation in the response time of pollutants to these transients and facility-specific differences suggest that such measures will require a timelagged correlation between PCDD/F and monitorable surrogate compounds that is statistically established for each particular facility.".

Reinmann: Continuous Monitoring of Unintentionally Formed POPs Listed Under the Stockholm Convention (PCDDs/PCDFs, PCBs, HCB) Using AMESA® Long Term Sampling System
2006 - Germany - "Because of the fact, that manual sampling can give only insufficient information of the total dioxin emissions due to a spot measurement of several hours during one year, the general wish is to have an on-line monitoring, which is however not yet possible. Therefore long term sampling with AMESA® is the practical choice for continuous monitoring of PCDD/PCDF emission from waste incinerators and other industrial emission sources."
"After a network of 12 AMESA monitors was installed in this region, the total dioxin emissions of 4 waste incinerators were reduced by a factor of 10, whereby up to now the quantity of the total burned waste was increased by almost 50 % (fig. 4)."
"The results of the present sampling tests show that the AMESA® sampling system can be used for long term monitoring of the full range of U-POPs (PCDD/PCDF, PCBs, HCB) listed under the Stockholm Convention. Furthermore the test revealed that the AMESA® system is capable to adsorb and hence monitor even molecules with higher volatility (pentachlorobenzene, tri– to pentachlorophenol). Since all POPs listed in Stockholm Convention are less volatile (Aldrine, Chlordane, DDT, Dieldrine, Endrine, Heptachlor, Mirex, Toxaphen) the AMESA® system has the potential to sample the full range of POPs. This indicates that the AMESA® system can be applied for monitoring and supervision of air emissions of POPs remediation projects and POPs destruction processes."

Reinmann: Cost Analysis of Automated Long-Term Sampling in Comparison to Existing Application Modes of Manual Short-Term Sampling
2004 - Germany - Cost comparison of manual stack test vs. AMESA CEM.
"Both examples from Taiwan and from Europe show that by higher sampling frequencies an automated sampling system is the more cost-efficient solution. Additional such an instrument is a really good tool to detect really the total yearly dioxin and furan emissions of a plant. Therefore quite more accurate dioxin emission inventories can be given by relatively low costs. Additionally such an instrument is suitable to optimize the operation of a plant with the effect, that the dioxin emissions could be reduced effectively, like it was shown several times over the last few years."

DeFre: Underestimation in Dioxin Emission Inventories
1998 - Belgium - There's discrepancy between dioxin levels in the environment and what is known to be emitted. Study found the discrepancy could be accounted for when considering the difference between stack-test estimates of dioxin emissions and two-week continuous emission tests. Continuous testing showed dioxin emissions 30 to 50 times higher than stack tests indicated.